**Question:** A 14 weeks pregnant female is found to have increased nuchal thickness on an ultrasound scan. In Down's syndrome, the 2nd trimester quadruple test includes all, EXCEPT:

A. Alpha-fetoprotein (AFP)
B. Beta-human chorionic gonadotropin (β-hCG)
C. Estriol
D. Inhibin A

**Correct Answer:**

**Core Concept:** Down's syndrome is a genetic disorder caused by the presence of an extra chromosome 21. This increases the risk of developmental abnormalities and developmental delay. The 2nd trimester quadruple test is a screening test used to identify pregnant women who are at higher risk of having a baby with Down's syndrome. The test measures the levels of four specific markers in the mother's blood: Alpha-fetoprotein (AFP), Beta-human chorionic gonadotropin (β-hCG), Estriol, and Inhibin A.

**Why the Correct Answer is Right:** In Down's syndrome screening tests, the levels of the markers are typically altered. The levels of AFP, β-hCG, and Estriol are typically elevated, while Inhibin A levels are typically decreased. However, Inhibin A is not significantly affected in Down's syndrome, making it the exception in this context.

**Why Each Wrong Option is Incorrect:**

**A.** Alpha-fetoprotein (AFP): In Down's syndrome, AFP levels are elevated.

**B.** Beta-human chorionic gonadotropin (β-hCG): In Down's syndrome, β-hCG levels are elevated.

**C.** Estriol: In Down's syndrome, Estriol levels are elevated.

**D.** Inhibin A: In Down's syndrome, Inhibin A levels are typically decreased but not significantly affected, making it the correct option in this question.

**Clinical Pearl:** The quadruple test, including Inhibin A, is useful in identifying women who are at higher risk for having a baby with Down's syndrome. However, in the context of Down's syndrome, Inhibin A is not significantly affected, which makes it the correct answer in this question. This test is usually performed between 15-20 weeks of gestation and is used to estimate the risk of having a baby with Down's syndrome.

**Why the Correct Answer is Right:** In Down's syndrome, the levels of AFP, β-hCG, and Estriol are elevated. Therefore, Inhibin A is the correct answer because it is typically decreased but not significantly affected by Down's syndrome. This is crucial information for understanding the results of the quadruple test and interpreting the risk for having a baby with Down's syndrome.

**Why Each Wrong Option is Incorrect:**

**A.** Alpha-fetoprotein (AFP): In Down's syndrome, AFP levels are elevated.

**B.** Beta-human chorionic gonadotropin (β-hCG): In Down's syndrome